Meteoroid detector

ABSTRACT

Use of a cold-cathode discharge tube with a gas-pressurized cell in space for recording a meteoroid puncture of the cell and for determining the size of the puncture.

United States Patent [191 McMaster et al.

Uct. 9, 1973 METEOROID DETECTOR Inventors: Leonard R. McMaster,

Williamsburg; Sheldon T. Peterson; Frank M. Hughes, both of Hampton, allof Va.

The United States of America as represented by the Administrator of theNational Aeronautics and Space Administration, Washington, DC.

Filed: Sept. 27, 1971 Appl. No.: 184,090

Assignee:

[56] References Cited UNITED STATES PATENTS 1,448,540 3/1923 Houskeeper324/65 R X 3,407,304 10/1968 Kinard et al. 73/12 X 3,446,068 5/1969Slattery et a1 73/12 X Primary Examiner-Richard C. Queisser AssistantExaminerStephen A. Kreitman Attorney--l-loward J. Osborn et a1.

[57] ABSTRACT Use of a cold-cathode discharge tube with a gaspressurizedcell in space for recording a meteoroid puncture of the cell and fordetermining the size of the 3 Claims, 1 Drawing Figure POWER SUPPLYRECORDING D.C. VOLTMETER PRESSURIZED CELL PATENTEI] [NIT 9 973 POWERSUPPLY RECORDING 11c. VOLTMETER g] [t I l2 l3 I9 PRESSURIZED CELLINVENTORS LEONARD R. McMASTER SHELDON T. PETERSON FANK M s s V v IATTORN S METEOROID DETECTOR ORIGIN OF THE INVENTION The inventiondescribed herein was made by employees of the United States Governmentand may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION The invention relates generally to meteoroiddetectors and more specifically concerns a meteoroid detector that notonly detects a meteoroid but also determines the size of the puncturecaused by the meteoroid.

The possible danger in an encounter between meteoroids and spacecrafthas resulted in various research activities designed to define themeteoroid environment in space and its effect on spacecraft. The moststraightforward way of determining meteoroid hazards to spacecraft isaccomplished by penetration techniques. One such technique employs asimple one-shot device referred to as a pressurized cell detector. Itconsists of a gas-pressurized cell equipped with a pressure sensor. Whena meteoroid punctures the cell, the gas leaks out and the loss ofpressure is detected by the pressure-sensitive device.

The pressure sensor presently used with the pressurized cell detector isa diaphragm-actuated microswitch. To date no attempt has been made todetermine the size of a puncture using these sensors, even though amethod exists as follows: two switches'are installed and set to actuateat different pressures, the time interval between their actuationsgiving the leak rate and, thereby, the size of the hole. The weight(0.78 Kg) and size (3.4 X lO m of these mechanical switches make theiruse in large quantities prohibitive and if penetration size is to beobtained, as well as a record of the event, their useis even moreundesirable as weight and volume are doubled.

A review of the proposed meteoroid population investigation throughinterplanetary space, using pressurized cell detectors, indicates a needfor a pressure sensor considerably reduced in weight and volume fromthose currently used.

It is therefore an object of this invention to provide a pressure sensorconsiderably reduced in weight and volume from those currently used tomonitor pressurized cell meteoroid detectors.

Another object of this invention is to provide a meteoroid detectorthatnot only detects a meteoroid but also determines the size of thepuncture caused by the meteroid.

Other objects and advantages of this invention will become apparenthereinafter in the specification and drawing.

SUMMARY OF THE INVENTION The invention includes a sensor for sensingpressure changes inside a gas-pressurized cell. The'pressure sensor is asimple cold-cathode glow discharge tube operating with an electricpotential applied across two electrodes. The pressure sensor is mountedon the gaspressurized cell such that the pressurized gas inside the cellis inside the tube. The potential applied across the two electrodes isinsufficient to cause a breakdown between the electrodes at the initialmolecular density within the cell. However, when the cell is puncturedby a meteoroid in space, gas will flow through the puncture into space.The gas density inside the tube will decrease to a value where adischarge, similar to that of a neon glow lamp, will take place. Theglow discharge tube operates like a pressure switch, indicating an opencircuit before a puncture and indicating a closed circuit, by allowing acurrent to flow between the electrodes, after a puncture. As the gasdensity within the detector cell continues to decrease after abreakdown, the current flow between the electrodes also decreases untilit can no longer be maintained. Recording the current flow through thedischarge tube then gives a time history of the events resulting fromthe puncture of a detector cell, i.e., a record of the gas leak rate;hence, the size of the puncture can be determined.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE in the drawing is aschematic diagram of an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the embodimentofthe invention selected for illustration in the drawing the number 11designates a cold-cathode glow discharge tube having electrodes 12 and13. These electrodes are enclosed by a pressure-tight wall 14. Electrode12 is connected through wall 14 to ground and to one side of variabled.c. voltage power supply 15. Electrode 13 is connected through wall 14,a resistor 16 and a variable resistor 17 to the other side of powersupply 15. A recording d.c. voltmeter 18 is connected across resistor16. The purpose of variable resistor 17 is to adjust the amplitude ofthe voltage recorded by voltmeter 18. Tube 11 is attached to apressurized cell 19, having walls 20. The enclosure of discharge tube 11is connected to the enclosure of cell 19 through an opening 21 such thatthe pressure inside tube 11 is the same as the pressure insidec'ell 19.Walls 20 are exposed to space and are made from any suitable materialthat will puncture when impacted with a meteoroid. A tube 22 and a valve23 are used for pressurizing cell 19 with any suitable gas, such ashelium.

In the operation of this invention power supply 15 is adjusted to somedesired level. Then variable resistor 17 is adjusted so that the voltageacross resistor 16 when tube 11 breaks down is within the range ofrecording d.c. voltmeter 18. Valve 23 is opened and .helium is pumpedthrough tube 22 until the pressure inside tube 11 and cell 19 is higherthan the breakdown pressure for the particular voltage setting of powersource 15. Valve 23 is then closed and cell 19 is put into space.Whenever a meteoroid punctures walls 20 of the helium inside cell 19begins to leak through the puncture into space. This continues until thepressure inside the cell and discharge tube decreases to a value where adischarge occurs. The resulting conduction produces a voltage dropacross resistor 16 which is recorded by voltmeter 18. The cold-cathodedischarge tube 11 has thus functioned like a pressure switch, indicatingan open circuit before a puncture and indicating a closed circuit byallowing a current to flow between electrodes 12 and 13 after apuncture. As the pressure within cell 19 continues to decrease afterbreakdown, the current flow between the electrodes will also decreaseuntil a discharge can no longer be maintained. Recording the event ofcurrent flow through discharge tube 11 by voltmeter 18 will give a timehistory record of the puncture of cell 19, i.e., a record of the heliumleak rate and, hence, the size of the puncture can be determined. Thelargest puncture whose size can be determined is a puncture the size ofopening 21. If a larger puncture occurs, tube 11 will see it as apuncture the size of opening 21.

The reason tube 11 acts as it does is that a gas in its normal state isalmost a perfect insulator, but when an electric field of sufficientintensity is created in the gas between two electrodes, the gas becomesa conductor. This transition from an insulating to a conducting state iscalled the electrical breakdown. The relationship between the breakdownvoltage and the gas pressure, known as Paschens law, exhibits a minimumbreakdown voltage at some medium pressure. At both higher and lowerpressures relatively large voltages are required for breakdown. Withoutthe increased electric field, the mean free path of the gas particles istoo short at the higher pressures for them to gain enough energy forionization between successive collisions. At the lower pressures themean free path is so long that the probability of any collision is verysmall.

There are two main advantages of this invention over the prior art.First, it provides a means for recording a meteoroid puncture of a celland for determining the size of the puncture; and second, by using acoldcathode discharge tube to perform these functions a great saving inboth weight and volume is obtained.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred embodiment. Various changes maybe made without departing from the spirit and scope of the invention asdefined in the subjoined claims. For example, a transmitter could beused in place of voltmeter 18 to transmit the history of the conductionof tube 11 to earth before it is recorded. The shapes and sizes of tubes11 and cell 19 can be different from those shown. And gases other thanhelium could be used as the pressurizing gas.

What is claimed is:

1. A method for detecting a meteoroid puncture in a cell and fordetermining the size of the puncture comprising the steps of:

attaching a cold-cathode discharge tube, having two electrodes, to saidcell such that said two electrodes are inside said cell;

applying a voltage across two electrodes;

pressurizing said cell with a gas to a level where there is noconduction between said two electrodes; placing said cell in a spaceenvironment; and recording a history of the conduction between said twoelectrodes whereby the event of a meteoroid puncture and the size of thepuncture can be determined from said recorded history.

2. Apparatus for detecting meteoroids in space and for measuring thepotential danger of the meteoroids detected comprising:

a cold-cathode discharge tube having two electrodes;

a potential source connected across said two electrodes;

means for recording a history of the conduction between said twoelectrodes;

a cell, and

means connecting the interior of the tube with the interior of the cell,a gas filling the tube, cell and connecting means, the gas beingpressurized to such an extent as to prevent conduction between said twoelectrodes and exposed to space so that when a meteoroid punctures saidcell the gas will leak into space decreasing the pressure to a valuewhere there is conduction between said two electrodes and thereafterfurther decreasing the pressure until there is no conduction betweensaid two electrodes whereby the history recorded by said recording meansindicates the event of a puncture and the size of the puncture.

3. Apparatus according to claim 2 wherein said gas is helium.

1. A method for detecting a meteoroid puncture in a cell and fordetermining the size of the puncture comprising the steps of: attachinga cold-cathode discharge tube, having two electrodes, to said cell suchthat said two electrodes are inside said cell; applying a voltage acrosstwo electrodes; pressurizing said cell with a gas to a level where thereis no conduction between said two electrodes; placing said cell in aspace environment; and recording a history of the conduction betweensaid two electrodes whereby the event of a meteoroid puncture and thesize of the puncture can be determined from said recorded history. 2.Apparatus for detecting meteoroids in space and for measuring thepotential danger of the meteoroids detected comprising: a cold-cathodedischarge tube having two electrodes; a potential source connectedacross said two electrodes; means for recording a history of theconduction between said two electrodes; a cell, and means connecting theinterior of the tube with the interior of the cell, a gas filling thetube, cell and connecting means, the gas being pressurized to such anextent as to prevent conduction between said two electrodes and exposedto space so that when a meteoroid punctures said cell the gas will leakinto space decreasing the pressure to a value where there is conductionbetween said two electrodes and thereafter further decreasing thepressure until there is no conduction between said two electrodeswhereby the history recorded by said recording means indicates the eventof a puncture and the size of the puncture.
 3. Apparatus according toclaim 2 wherein said gas is helium.